As an overcurrent protection device, a technique described in JP 2016-082806 A (Reference 1) is known.
The overcurrent protection device described in Reference 1 is provided in a switching circuit, which forms an output voltage. The overcurrent protection device includes a voltage monitoring unit and a current monitoring unit. The voltage monitoring unit monitors a voltage formed by the output stage of the switching circuit. The current monitoring unit monitors current flowing through the output stage of the switching circuit.
By the way, in the technique described in Reference 1, the overcurrent protection device stops a switching operation when the voltage of the output stage exceeds a threshold value. In addition, the overcurrent protection device stops a switching operation when the voltage of the output stage is lower than a threshold value and overcurrent exceeds a threshold value. That is, when the voltage of the output stage is lower than the threshold value, it is determined whether or not the current is overcurrent according to whether or not the current exceeds the threshold value.
In a drive device that drives, for example, a motor, a voltage input to a switching circuit varies. Meanwhile, overcurrent in the motor also varies depending on the magnitude of the applied voltage. Therefore, in a case where the voltage varies, when determining overcurrent based on a current reference as to whether or not current exceeds a threshold value, there is a risk of erroneously determining overcurrent even if this determination is performed under a condition that the voltage is lower than a predetermined threshold value. Due to this, there is a risk of unnecessarily stopping the switching circuit, and in some cases, protection of the motor may not be appropriate.